impalpable (adj.)

c. 1500, "too unsubstantial to be perceived by touch," from French impalpable or directly from Medieval Latin impalpabilis, from assimilated form of in- "not, opposite of" (see in- (1)) + palpabilis (see palpable). Figurative (mental) sense of "that cannot be grasped by the intellect" is from 1774. Related: Impalpably; impalpability.